Electrically insulated double tube heat pipe arrangement

ABSTRACT

For cooling a heat source, such as a component part of electronic equipment which has a high electrical potential, a heat pipe arrangement is employed which is formed of a closed first pipe or tube in contact with the heat source and a closed second pipe or tube enclosing the first tube. A capillary structure of a metallic material is formed on the inner surface of the first tube and a similar capillary structure also of a metallic material is formed on the outer surface of the first tube and acts as a part of the capillary structure within the second tube. On the inner surface of the second tube, spaced outwardly from the capillary structure on the outer surface of the inner tube, is another capillary structure connected by a bridging member formed of an electrical insulating material, to the capillary structure on the outer surface of the inner tube to permit condensation to flow from the capillary structure on the outer tube to that on the inner tube. Similarly, a bridging member is provided within the inner tube for the same purpose, the vaporizable working medium within the inner tube is either water or a metal while the working medium within the outer tube is a vaporizable dielectric liquid.

Unite States Patent 1191 Gammel et al.

1451 Aug. 6, 1974 Heidtmann, Nussloch; Mattias Jiins, Heidelberg, all of Germany [73] Assignee: Brown, Boveri & Cie AG,

Mannheim, Germany 22 Filed: Apr. 20, 1972 21 Appl. No.: 245,827

Primary Examiner-Albert W. Davis, Jr. Attorney, Agent, or Firm-Toren, McGeady and Stanger 7 ABSTRACT For cooling a heat source, such as a component part of electronic equipment which has a high electrical potential, a heat pipe arrangement is employed which is formed of a closed first pipe or tube in contact with the heat source and a closed second pipe or tube enclosing the first tube. A capillary structure of a metallic material is formed on the inner surface of the first Fm'eign Application Priority Data tube and a similar capillary structure also of a metallic Apr. 27, 1971 Germany 2120477 ria s rmed n the outer surface of the first tube and acts as a part of the capillary structure within [52] U.S. Cl. 165/105, 317/234 B, 174/15, h e nd be. 0n h inner surface of the second 313/12, 313/18, 313/26, 313/ tube, spaced outwardly from the capillary structure on [51 1 Int. Cl. F28d 15/00 the Outer Surface of the inner tube, s oth cap llary [581 Field of Search 165/ 317/234 B; structur c nnected y a bridging member formed of 174/15; 313/12, 18, 26, 45 an electrical insulating material, to the capillary structure on the outer surface of the inner tube to permit [56] References Cited condensation to flow from the capillary structure on UNITED STATES PATENTS the outer tube to that on the inner tube. Similarly, a bridging member is provided within the inner tube for S1 2: the same purpose, the vaporizable working medium 3'54384] 2/1970 65/105 X within the inner tube is either water or a metal while 3:563:30) 2/1971 Basiulis /105 the Working medium Within the Outer tube is a p FOREIGN PATENTS OR APPLICATIONS able d'elecmc f 1.953.501 6/1970 Germany 165/105 8 Clam, 2 Drawmg Flgures ELECTQ/C ELECrQ/CAALV COA/DUC 771 5 fiz MAE-O/UMA Wa /(0V6 MED/UM 74 7E4l EL/IV6 14 41 4- fuss caLLr-zcroe 1 a 4- i I1 3 1,

72 1 18 i HEcne/CQLLY A //I/$(/L,977/V6 I. X Q4P/LL44ey Wl7Z'e/4L 2 \CWP/LLA'EV STEUCTUEE l0 .9

ELECTRICALLY INSULATED DOUBLE TUBE HEAT PIPE ARRANGEMENT SUMMARY OF THE INVENTION The present invention is directed to an electrically insulated heat pipe arrangement for removing high heat flux densities from heat sources which have a high electrical potential, such as component parts of electronic equipment, and, more particularly, it concerns a heat pipe formed of an inner tube enclosed within an outer tube with a different working medium in each of the tubes.

As is known, a heat pipe is a closed vacuum-proof tubular vessel containing a capillary structure and partially filled with a vaporizable liquid working medium which is conveyed through the vessel by the capillary structure. Heat is absorbed on one side of the heat pipe,

that is on its heat-receiving surface, and the absorbed heat vaporizes the liquid working medium. The evaporated liquid flows to the opposite side of the heat pipe, that is to a heat delivering surface, where it is condensed. By means of the capillary structure the condensed working medium is returned from the heat delivering surface to the heat receiving surface. By means of such a heat pipe, relatively large quantities of heat can be transported at slight temperature differences between the heat-receiving and the heat-delivering surfaces. Such heat pipes can be used for cooling semiconductor components, transmitting tubes, travelingwave tubes and the like.

If the heat-receiving and the heat-delivering surfaces are to be on a different electric potential, the working liquid must be a dielectric material. Additionally, between the heat-receiving and the heat-delivering sur faces of the heat pipe there must be an electrically insulating zone which is not electrically bridged by the working medium.

In dielectric working media, however, the heat transfer upon evaporation is much lower than other working media, for instance water or metals. Further, the maximum heating surface load to the film boiling limit of dielectric liquids is at least half that as for water. Compared with metals, the relationship may be in the range of H20.

The cooling of traveling-wave tubes with electrically insulated heat tubes is known. The electron capture member of the tube is cup-shaped and forms, at the same time, the heating zone of the heat pipe. The electron capture member is electrically separated from the rest of the tube by a ceramic material. Since there is a voltage drop between the outer shell of the heat pipe, that is its heat-delivering surface, and the electron capture member, that is the heat-receiving surface the electron capture member is on high voltage while the heat delivering surface is grounded an insulating zone must be provided between the heat-delivering surface and the heat-receiving surface. Therefore, the capillary structure used within the heat pipe for improving the transport of the working medium must be an electrical insulating material. Dielectric liquids are used as the working medium for such heat pipes. However, the use of such dielectric liquids has considerable disadvantages. If, for example, a silicone oil is used as the working medium, ebullient boiling can be attained at the heat-receiving surface at a maximum attainable heat current of 20 watts per square centimeter, the

temperature difference between the pipe wall and the working medium, that is the temperature difference within the liquid film at the heat-receiving surface, is 150 C. The use of such a heat pipe is not advantageous because the isothermal heat transport is entirely absent. If, instead of silicone oil, water is used as the working medium, it would be possible to attain a maximum heat current for ebullient boiling of 140 watts per square centimeter and a temperature difference within the liquid film at the heat-receiving surface of l4 C.

Therefore, a primary object of the present invention, is the provision of a heat pipe arrangement capable of removing large quantities of heat for cooling heat sources having a high electric potential, for example, semi-conductor components, where the temperature difference between the heat-receiving and the heatdelivering surfaces is substantially reduced. Further, the heat-receiving surface and the heat-delivering surface each have a different electric potential.

In accordance with the present invention, the problem experienced in the past is overcome by using a heat pipe formed of at least two closed heat tubes, one enclosed within the other so that the heat-delivering surface of the inner heat tube acts as the heat receiving surface for the outer heat tube. Further, the inner heat tube uses, as the working medium, water or a metal, while the outer heat tube uses a dielectric liquid as the working medium. In providing the enclosure of the inner tube by the outer tube, the tubes are mechanically interconnected by an insulating member and the capillary structure within the outer heat tube is made 7 of an electrical insulating material.

Within the outer heat tube, bridging members extend between the capillary structure on the inner surface of the outer tube and the capillary structure on the outer surface of the inner tube so that the condensed liquid medium can flow from the heat-delivering surface to the heat-receiving surface. Further, to afford the desirable insulating characteristics in the heat pipe, the bridging members are formed of a good electrical insulating material.

A preferred use of such a double heat tube heat pipe arrangement is in cooling electronic components, such as semi-conductor elements and the like used in grounded operations. Moreover, due to the specific weight of the arrangement, it is also possible to use the heat pipe arrangement in accordance with the present invention for cooling heat-generating components in aircraft and spacecraft vehicles.

The inner heat tube of the heat pipe arrangement contains a working medium which absorbs a high heat flux density at a small temperature gradient. Due to the fact that the heat-delivering surface of the inner heat tube is, at the same time, the heat-receiving surface for the outer heat tube, the heat flux density transferred into the outer heat tube containing the dielectric liquid working medium may be small, since the heat-receiving surface of the outer tube is relatively large. The temperature gradient between the heat-receiving surface and the heat-delivering surface of the outer tube will, as a result, be very small.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWING DETAILED DESCRIPTION OF THE INVENTION In FIG. 1, a heat pipe arrangement is shown for use with a traveling-wave tube, and the arrangement consists of an inner heat tube 1 enclosed laterally and at its ends by an outer heat tube 2. One end of the inner heat tube forms a heat-receiving surface 3 having a cupshaped configuration for receiving the collector 4 of a traveling-wave tube 13. Accordingly, the collector 4 serves as a heat-receiving surface for the inner heat tube 1. Formed on the interior surface of the inner heat tube] is a capillary structure 5 formed of a metallic material and containing, as the heat pipe working medium, a vaporizable liquid such as a metal or water with which high heating surface loads are attainable. The portion of the inner tube which does not act as the heat receiving surface 3, that is the part in spaced relationship to the collector 4, provides a heat-delivering surface 6 for the inner tube. To improve the passage of condensation from the capillary structure 5 contacting the heat-delivering surface 6 to the capillary structure 5 in contact with the heat-receiving structure 3, a bridging member 7 formed of the same capillary material as the capillary structure 5 extends between the different portions of the capillary structure 5. The heatdelivering surface 6 is completely enclosed by the second heat tube 2 and, as a result, it serves as the heatreceiving surface for the outer heat tube. On the outer surface of the inner heat tube, that is within the outer heat tube, a capillary structure 8 of metallic material is formed. Opposite the capillary structure 8 another capillary structure 9 is formed on the inner surface of the outer heat tube 2 and a number of bridging members 10 formed of an electrically insulating capillary material extend between the two capillary structures 8 and 9 for affording the passage of condensation from the heat-delivering surface to the heat-receiving surface. The inner tube 1 and the outer tube 2 are mechanically interconnected by means of a insulating section 11 located adjacent the end of the inner tube forming its heat-receiving surface. Radially outwardly from the insulating section 11 and extending between the inner capillary structure 8 and the outer capillary structure 9 of the outer tube is another bridging member 12 formed of an electrically insulating capillary material which affords the same function as the bridging members 10.

The operation of the heat pipe arrangement described above is as follows. I

Heat from the collector of the traveling-wave tube 13 is absorbed by the heat-receiving surface 3 of the inner heat tube 1. The heat passing through the heatreceiving surface causes the vaporizable liquid working medium, either water or a metal, within the capillary structure 5 adjoining the heat-receiving surface to vaporize and flow through the tube to the capillary structure adjoining the heat-delivering surface 6 of the inner tube. Within the capillary structure, the vaporized working medium condenses and its heat is transferred into the heat-delivering surface 6 of the inner tube which also acts as the heat-receiving surface of the outer tube 2. Within the outer tube the vaporizable dielectric liquid within the capillary structure 8 is evaporated by the heat received from the inner tube and the vaporized working medium flows through the tube to the capillary structure 9 on its heat delivering surface. Within the capillary structure 9 the vaporized working medium condenses and flows back over the bridging members 10 and 12 to the capillary structure 8 on the heat-receiving surface 6 of the outer tube 2. Heat can be removed from the exterior surface of the outer tube 2 by means of radiation or by a liquid or gaseous coolant contacting the outer surface. To avoid any gas discharge, the outer heat tube 2 contains a buffer gas, for example, SP which is stored in a separate tank and suppliedinto the outer tube via the conduit 14 or it can be stored within the outer heat tube itself. An important advantage of this heat pipe arrangement is that water or metal may be used as the working medium within the inner heat tube, accordingly, with such a working medium, high heat absorption rates at approximately constant temperature are effective at the heat receiving surface of the inner tube.

In the example shown in FIG. 1, the heat absorption rate can be increased to 140 watts per square centimeter with a temperature gradient within the liquid film in the capillary structure at the heat-receiving surface of only l4 C. Therefore, instead of a very small surface on the collector acting as the heat-receiving surface, a much larger heat-delivering surface of the inner heat tube can be used for transmitting heat to the dielectric working medium within the outer heat tube.

In the following example, the reduction of the temperature difference-between the heat-receiving surface and the heat-delivering surface in an arrangement with one heat tube or pipe is compared tothat of the present arrangement which utilizes two heat tubes, one within the other as the heat pipe arrangement. In the single tube arrangement as the dielectric working medium a fluorine-carbon compound is used, while in the double tube arrangement water is used in the inner tube and the same fluorine-carbon compound provides the dielectric working medium in the outer tube. In the first instance, at a heat flux density of watts per square centimeter, a temperature gradient within the liquid film of the working medium of 200 C. will result at the heat-receiving surface. By comparison, in the arrangement of the present invention, using water as the working medium, it is possible to obtain a temperature gradient of 8 C. for the same heat flux density. If the heatdelivering surface of the inner tube, which is also the heat-receiving surface of the outer tube, is increased by a factor of 20 as compared to the heat-receiving surface of the inner tube, there results in the dielectric working medium in the outer tube a temperature gradient of 40 C. As a result, in the first instance the total temperature gradient is 200 C. while in the second in stance it is only 48 C.

In FIG. 2, another design of the present invention is illustrated, where the heat-receiving surface of the inner tube 1 lies in the same plane withone of the end surfaces of the outer tube 2. The heat receiving surface 3 of the inner tube 1 is in contact with a disk cell of a thyristor for absorbing the heat from the disk cell. Though the inner cell in FIG. 2 does not have the cupshaped configuration at its receiving surface as in the embodiment shown in FIG. 1, the remaining structure of the inner tube 1 and the outer tube 2 is the same as in FIG. 1 and the same reference numerals are employed, however, there is no bridging element 7 provided within the inner tube 1. The heat absorbed from the disk cell 15 causes the working medium within the capillary structure 5 at the heat receiving surface 3 to vaporize and flow through the tube to the remaining portions of the capillary structure which are in contact with the heat-delivering surface 6 of the inner tube which also serves as the heat-receiving surface of the outer tube 2-. Accordingly, the relatively small surface provided by the heat-receiving surface 3 removes the heat from the disk cell 15 and transfers it to the relatively large remaining surface of the inner tube which acts as the heat-receiving surface for the outer tube.

What is claimed is:

1. An electrically insulated heat pipe arrangement for high heat flux densities for cooling heat surfaces which have a high electric potential, such as component parts of electronic equipment, comprising a first axially extending tube closed at its ends and having a first closed space therewithin, a second axially extending tube closed at its ends and laterally enclosing said first tube, said second tube forming in combination with the outer surface of said first tube a second closed space completely enclosing at least the sides and one end surface of said first tube, a first capillary structure lining the interior surface of said first tube, a second capillary structure formed on the outer surface of said first tube and located within said second space, a third capillary structure formed on the interior of said second tube and spaced from said second capillary structure, a vaporizable electrically conductive working medium located within said first space in said first tube, a vaporizable dielectric working medium located within the second space in said second tube and maintained separate from said vaporizable working medium located in said first space, said electrically conductive working medium within said first space being capable of absorbing a considerably higher heat flux density than the dielectric working medium in said second space, an electrically insulating section located within said second space and separating and mechanically connecting said first tube and said second tube together, a fourth capillary structure located within said second space formed of an electrically insulating material and extending between said second capillary structure and said third capillary structure, and said first tube arranged to act as a heat transfer surface for withdrawing heat from a component part and supplying the withdrawn heat into said second space with one portion of the surface of said first tube acting as a heat-receiving surface for said first space and a separate portion of said first tube which is completely enclosed by said second tube acting as the heat-delivering surface for said first space and as the heat-receiving surface for said second space.

2. An electrically insulated heat pipe arrangement, as set forth in claim 1, wherein said working medium in said first space is water.

3. An electrically insulated heat pipe arrangement, as set forth in claim 1, wherein said working medium in said first space is a vaporizable liquid metal.

4. An electrically insulated heat pipe arrangement, as set forth in claim 1, wherein said first tube has a cupshaped recess formed in one end surface thereof and said recess acting as the heat-receiving surface for said first space for removing heat from the component part.

5. An electrically insulated heat pipe arrangement, as set forth in claim 4, wherein a bridging member formed of the same capillary material as said first capillary structure is located within said first tube and extends from said first capillary structure in contact with said cup-shaped recess to a location on said first capillary structure spaced from 'said cup-shaped recess.

6. An electrically insulated heat pipe arrangement, as set forth in claim 5, wherein said first capillary structure and said bridging member are formed of a metallic material.

7. An electrically insulated heat pipe arrangement, as set forth in claim 1, wherein at least one bridging member formed of an electrically insulating capillary material interconnects said second and third capillary structures so that said bridging member affords a return flow of condensation from said third capillary structure to said second capillary structure.

8. An electrically insulated heat pipe arrangement, as set forth in claim 1, wherein a conduit is connected to said second tube and communicates with the space therein between said first and second tubes for supplying a buffer gas thereto. 

1. An electrically insulated heat pipe arrangement for high heat flux densities for cooling heat surfaces which have a high electric potential, such as component parts of electronic equipment, comprising a first axially extending tube closed at its ends and having a first closed space therewithin, a second axially extending tube closed at its ends and laterally enclosing said first tube, said second tube forming in combination with the outer surface of said first tube a second closed space completely enclosing at least the sides and one end surface of said first tube, a first capillary structure lining the interior surface of said first tube, a second capillary structure formed on the outer surface of said first tube and located within said second space, a third capillary structure formed on the interior of said second tube and spaced from said second capillary structure, a vaporizable electrically conductive working medium located within said first space in said first tube, a vaporizable dielectric working medium located within the second space in said second tube and maintained separate from said vaporizable working medium located in said first space, said electrically conductive working medium within said first space being capable of absorbing a considerably higher heat flux density than the dielectric working medium in said second space, an electrically insulating section located within said second space and separating and mechanically connecting said first tube and said second tube together, a fourth capillary structure located within said second space formed of an electrically insulating material and extending between said second capillary structure and said third capillary structure, and said first tube arranged to act as a heat transfer surface for withdrawing heat from a component part and supplying the withdrawn heat into said second space with one portion of the surface of said first tube acting as a heat-receiving surface for said first space and a separate portion of said first tube which is completely enclosed by said second tube acting as the heatdelivering surface for said first space and as the heat-receiving surface for said second space.
 2. An electrically insulated heat pipe arrangement, as set forth in claim 1, wherein said working medium in said first space is water.
 3. An electrically insulated heat pipe arrangement, as set forth in claim 1, wherein said working medium in said first space is a vaporizable liquid metal.
 4. An electrically insulated heat pipe arrangement, as set forth in claim 1, wherein said first tube has a cup-shaped recess formed in one end surface thereof and said recess acting as the heat-receiving surface for said first space for removing heat from the component part.
 5. An electrically insulated heat pipe arrangement, as set forth in claim 4, wherein a bridging member formed of the same capillary material as said first capillary structure is located within said first tube and extends from said first capillary structure in contact with said cup-shaped recess to a location on said first capillary structure spaced from said cup-shaped recess.
 6. An electrically insulated heat pipe arrangement, as set forth in claim 5, wherein said first capillary structure and said bridging member are formed of a metallic material.
 7. An electrically insulated heat pipe arrangement, as set forth in claim 1, wherein at least one bridging member formed of an electrically insulating capillary material interconnects said second and third capillary structures so that said bridging member affords a return flow of condensation from said third capillary structure to said second capillary structure.
 8. An electrically insulated heat pipe arrangement, as set forth in claim 1, wherein a conduit is connected to said second tube and communicates with the space therein between said first and second tubes for supplying a buffer gas thereto. 